The present invention relates to cargo aircraft, and, in particular, relates to those which drop their cargo by parachute.
Dropping cargo from aircraft encompasses several techniques. In the first technique, the aircraft has a rear door which when opened exposes a ramp inside the aircraft. The aircraft may fly at a low altitude near a drop point and someone in the aircraft just pushes the cargo out of the aircraft. This technique clearly requires that the cargo be either well padded or nonfrangible. This also requires that the aircraft reach a sufficiently low altitude for this technique to work and would not work in a mountainous area. Other considerations would be foliage. A higher altitude may be used but this would require extensive padding for the cargo to survive the drop.
Another technique requires the use of a parachute for the cargo. Because of the tremendous forces involved in the extraction of the cargo from the aircraft, the main drop parachute is usually deployed from the aircraft by means of a drogue chute. This is a much small parachute which is deployed, normally by hand. The ability to hit a drop zone requires much practice because of the many factors involved: the aircraft speed, the wind direction, the launching of the drogue chute, the time for it to deploy, the time to pull the cargo from the aircraft bay, the time for the main parachute to open, the weight of the cargo, etc.
In order to eliminate a number of these variables, a towplate assembly has been used in performing airdrop missions. The towplate is located in the rear of the bay. The clrogue chute is attached to one end of the extraction link and the cargo chute(s) to the other end. The main parachute is attached to the cargo and deploys after the cargo is pulled from the bay by the main parachute. Because of the tremendous forces involved as the drogue chute is towed by the aircraft, the extraction link, although electro-mechanically held in place, is not removed in a predetermined manner due to design problems, i.e., upon command from the cargo master.
The present towplate uses an overcenter technique that prevents a towed parachute from prematurely pulling the towlink out of the towplate thereby initiating the cargo extraction. The deficiency with this approach is that the towlink must be precisely manufactured in order to ensure that the overcenter condition occurs when the towlink is installed in the towplate assembly. In fact, the prior device has experienced premature cargo releases as a result of the towlink being pulled out of the towplate assembly. The cause of this problem has been identified as variations in the towlink specification.
Thus, there exists a need for a towplate positive lock device which insures that the cargo is released on time irrespective of minor variations in the specifications of the towlink.